Abstract Cirrhosis of the liver is among the top ten leading causes of death in the US, with more than 35,000 deaths each year. A major underlying cause of cirrhosis is liver injury associated with liver fibrosis; the pathological indication of cirrhosis is the development of scar tissue that replaces normal parenchyma. The scar tissue blocks the flow of blood through the liver, raising blood pressure and disturbing normal function. Current drugs that treat fibrosis are not always effective. Patients are often left with ?lifestyle modifications? that are difficult to sustain, and, at best, put patients in a race against disease progression. Small molecule agonists of the cannabinoid receptor CB2 have reduced liver fibrosis in several established animal models. CB2 agonists achieve this by inhibiting hepatic immune cells and hepatic stellate cells. CB2 agonism is a promising mode of action for treating liver fibrosis. However, small molecule CB2 agonists have drawbacks that undercut their effectiveness and safety, including cross-reactivity with CB1, crossing the blood- brain barrier and cross-activating CB1, causing the adverse cognitive effects of cannabinoids and rapid elimination from the body. A highly specific CB2 agonist antibody that is long-lived and restricted to peripheral tissues would be an ideal drug to test the CB2 agonism mode of action. Abalone Bio proposes 3 aims to test the feasibility of using CB2 agonist antibody drugs to treat liver fibrosis. (1) Engineer, produce, characterize CB2 agonist antibodies. VHH-Fc versions of identified hits will be made and characterized using multiple non-liver in vitro cell-based assays. (2) Assess effects of CB2 agonist antibodies on liver cells. In this aim, the antibodies from Aim 1 will be used to characterize anti-fibrotic effects in primary liver cells and stable liver cell lines in vitro. The data will bridge receptor pharmacology in standard cell lines with in vivo data from Aim 3 and can validate and expand biomarkers for fibrosis. (3) Assess anti-fibrotic effects of a CB2 agonist antibody in an in vivo model of liver fibrosis (with leading liver fibrosis expert and Consortium PI, Dr. Scott Friedman). This aim will test the feasibility of using CB2 agonism to treat liver fibrosis in thioacetamide rat models by measuring the effects of the antibody on blood markers, collagen levels, histopathology metrics, and gene expression. Success in the Phase I project will lead to a safe and effective drug for liver fibrosis, increase scientific understanding of liver disease, and define non-invasive biomarkers to monitor disease progression. Phase II (including IND-enabling studies) will involve selecting and optimizing a lead antibody, with a focus on good clinical and manufacturing attributes. This research will enable Abalone Bio to expand the impact of its CB2 antibody agonist drugs to other diseases involving fibrosis and inflammation, e.g., skin and lung diseases such as scleroderma and idiopathic pulmonary fibrosis.